Earlier quoted context omitted.
What are we to do? We build data visualization software, but firefox is REALLY slow at rendering SVG (so no d3 for us). We have a choice of asking our customers to run ie11 or chrome, since both run quickly. We would recommend firefox, since we really like the Mozilla foundation, but the performance of it is so bad we have to steer people away from it. It is a sad state of affairs.
If you make software (which people want to use, of course) and notice a mainstream open source browser (in this case Firefox) being slow at something in particular, wouldn't it be advantageous to you and everyone else if some of you could briefly look under the hood to see what the problem is? Maybe not fix the bug, but at least let Mozilla know that there is a pain point somewhere (perhaps with specific source files…
I once checked out chromium in order to test out whether file writing would be easy to do. The size of the project alone meant it took me forever to find out where to patch it.
(Edit: This was something like 5 years ago before I started to grow a distaste for Chrome)